Use "co_consts" in docstring detection.

Note: this is an upheaval because we need to pass "code" or at least
"code.co_consts" to the docstring detection routine

test/simple_source/bug27+/01_module_doc.py

@@ -0,0 +1,9 @@
+# From 2.7.17 test_bdb.py
+# The problem was detecting a docstring at the begining of the module
+# It must be detected and change'd or else the "from __future__" below
+# is invalid.
+# Note that this has to be compiled with optimation < 2 or else optimization
+# will remove the docstring
+"""Rational, infinite-precision, real numbers."""
+
+from __future__ import division